Pineapple Express: Watch the 'atmospheric river' roar [GIF]

The swoop and swirl of the California storm is depicted in neon green in the GIF below.

The so-called Pineapple Express is better described as an "atmospheric river," up to 400 miles wide, experts say. At its most ferocious, an atmospheric river can stall over an area, bringing extreme rainfall and floods, according to the National Oceanic and Atmospheric Administration.

There was ferocity with the storm that pummeled Northern California Thursday before wreaking havoc Friday in Southern California.